火花放电辅助-激光诱导击穿光谱技术中的放电通道特性研究

Characteristics of Discharge Channel in Spark Discharge Assisted Laser-induced Breakdown Spectroscopy

以门控脉冲高压电源作为火花放电电源,研究了火花放电辅助-激光诱导击穿光谱中放电通道与火花放电相对于激光脉冲之间延时的关系.研究结果表明:在合理的剥离激光能量和电极空间布置下,调节该延时可以实现由"V"字形放电到平行放电的转变.在"V"字形放电时,火花放电会扩大烧蚀坑洞的直径、破坏横向空间分辨率;而在平行放电情况下,火花放电不会扩大烧蚀坑洞的直径,从而保证其横向空间分辨率仅由激光剥离来决定.在平行放电的条件下开展了铝合金中铬元素的火花放电辅助-激光诱导击穿光谱定量分析,其检出限达到了8.8ppm,比单纯的激光诱导击穿光谱技术的分析结果改善了8倍.在火花放电辅助-激光诱导击穿光谱技术中采用带外触发控制的火花放电模式,可以实现平行放电和高横向空间分辨的样品表面元素分析.

The relationship between the discharge channel and the time delay between the spark discharge and the laser pulse in spark discharge assisted laser-induced breakdown spectroscopy was investigated by using a gate-able pulsed high-voltage power source as the power supplier of the spark discharge. It was demonstrated that under suitable laser pulse energy and geometrical arrangement of the electrodes, it was possible to change the discharge channel from ＂V-shaped＂ type to parallel type by adjusting this time delay. In the ＂V-shaped＂ discharge, the spark discharge was able to increase the diameters of the craters and deteriorate the lateral resolution. However, in the parallel discharge, the spark discharge did not increase the diameters of the craters ensuring that the spatial resolution in this technique was only determined by laser-ablation. Under the condition of parallel discharge, quantitative analysis of chromium in aluminum alloy with spark discharge assisted laser-induced breakdown spectroscopy was carried out and the limit of detection of chromium reached 8.8 ppm, which was 8 times better than that obtained in LIBS without the assistance of the spark discharge. By using spark discharge under external trigger mode in the spark discharge assisted laser-induced breakdown spectroscopy, it is convenient to realize parallel discharge and surface elemental analysis of samples under high spatial resolution.